heathkit hp-23b power supply restoration

Published May 4, 2017

Last night I finished restoring the hp-23b power supply that I got with the heathkit hw-101. You could tell that it hadn’t been used in a long time and it had all of the original components including the old paper caps. I never actually turned it on in its original state so I never verified if it was in working order, but it seemed like a no brainer to just go ahead and replace everything.

Here are the before pictures.

First, I ordered suitable replacement components from digikey. The parts numbers and quantities are below:

There is an additional 1k and 27k resistor that can be replaced as well, but I didn’t have any at the time and the original resistors were still in spec so I reused them.

Next, I disassembled the power supply. Luckily, the power supply and the hw-101 came with the original manuals, so disassembly and reassembly was very easy.

I collected all of the hardware and soaked everything in a vinegar bath for a few days to remove the rust.

I wanted to keep the stock look, so I took the old capacitors and removed the paper sleeve and then cut open the can.

After cleaning out all of the junk inside, I drilled small holes for the leads in the bottom of the can and soldered the leads to the original capacitors terminals.

Then I taped the can back together and replaced the paper sleeve.

Next up: paint. I went with a slightly different color from the original heathkit bluish-green color. I went with a can of rustoleum moss green.

I masked off the silkscreened labels on the front and then did several coats on the main chassis, the bottom plate, and the cover.

I also disassembled the main transformer and the choke and painted them black.

I clear coated everything and started putting it back together.

I flipped it over and rewired everything following the steps in the manual.

Once it was all together, I jumped the AC SW and AC Common terminals with a piece of wire and hooked it up to a variac and slowly brought up the voltage, watching its output. Everything seemed to work as expected. The low voltage, high voltage, and filament voltages were all where they should be.

I will probably clean up the wiring a bit and maybe hot glue a few things in so that there is less chance of anything shorting. Then I’ll button it up and start on the hw-101.